In resent years, multifunction and miniaturization have been advanced for portable devices such as portable phones. Semiconductor chips are arranged with high density in an enclosure of a miniaturized portable phone. A gap between the enclosure and the semiconductor chips is getting narrower. As a result, heat generated in the semiconductor chips or the like is immediately transferred to the enclosure.
The transfer of the heat generated in the semiconductor chips to the enclosure causes a rise of the temperature of the enclosure. Therefore, a heat dissipating structure is proposed to prevent high temperature of the enclosure.
As such heat dissipating structure, there are known techniques for suppressing a rapid rise in temperature, in which a shape memory alloy member or the like connected to a heat generating body is deformed to contact a heat. dissipating member (e.g. Japanese Laid Open Utility Model Application (JP-U-Heisei 2-73788), Japanese Laid Open Utility Model Application (JP-U-Heisei 4-25290), Japanese
Laid Open Utility Model Application (JP-U-Showa 62-73595), Japanese Laid Open Utility Model Application (JP-U-Heisei 4-34743), and Japanese Laid Open Patent Application (JP-P2002-124224A)).
Furthermore, as another heat dissipating structure, there are techniques using thermal storrage medium which changes from solid to liquid (Japanese Laid Open Patent Application (JP-P2004-152895A) , Japanese Laid Open Patent Application (JP-P2006-100564A) , Japanese Laid Open Patent Application (JP-P2001-274580A) , Japanese Laid Open Patent Application (JP-A-Heisei 11-202979) , and Japanese Laid Open Patent Application (JP-P2003-142864A)) . Furthermore, Japanese Utility Model Registration No. 3125565 discloses a material of such thermal storrage medium.
Disclosures in Japanese Laid Open Patent Application (JP-P2004-152895A) and Japanese Laid Open Patent Application (JP-P2006-100564A) out of these documents will be explained below.
FIG. 1 shows a heat dissipating structure disclosed in Japanese Laid Open Patent Application (JP-P 2004-152895A). This heat dissipating structure includes a plurality of heat generating bodies 102 mounted on a board 101, a sheet-like heat transfer member 104 arranged in close contact with the surfaces of the plurality of semiconductor chips 102, and a heat absorbing member 103 arranged in close contact with the surface of the heat transfer member 104 and configured to absorb heat transferred from the heat generating bodies 102 to the sheet-like heat transfer member by changing from solid phase to liquid phase. It is described that the heat dissipating structure is applied to a portable phone as shown in FIG. 2. According to the heat dissipating structure, temperatures of the plurality of the heat generating bodies 102 can be leveled and the heat generated in the heat generating bodies can be absorbed by the heat absorbing member.
However, according to the structure, since most of heat generated in the heat generating bodies is absorbed by the heat absorbing member, heat absorption by the heart absorbing member easily reaches saturation. Moreover, once the heat absorption by the heat absorbing member reaches saturation, heat absorbed in the heat absorbing member is dissipated from a heat dissipating portion such as an enclosure for a long time even after the heat generating bodies stop generating heat. Consequently, a user feels discomfort.
FIG. 3 shows a heat dissipating structure disclosed in Japanese Laid Open Patent Application (JP-P2006-100564A). FIG. 3 shows an enclosure 106, boards 107, electronic parts 108 mounted on the boards 107, and a thermal storrage medium 109 coated on an inner surface of the enclosure 106. According to the heat dissipating structure, heat transfer to an outer surface of the enclosure 106 in a short time can be prevented by the thermal storrage medium 109.
However, even if the heat dissipating structure is used, the thermal storrage medium reaches thermal saturation in a short time and heat stored in the medium is dissipated from the outer surface of the enclosure for a long time. Consequently, a user feels discomfort.